One who vouches, or gives witness or full attestation, to
anything.

A book, paper, or document which serves to vouch the truth
of accounts, or to confirm and establish facts of any kind; also, any
acquittance or receipt showing the payment of a debt; as, the
merchant’s books are his vouchers for the correctness of his accounts;
notes, bonds, receipts, and other writings, are used as vouchers in
proving facts.

The tenant in a writ of right; one who calls in another to
establish his warranty of title. In common recoveries, there may be a
single voucher or double vouchers.